A common method for making a road in a rural area involves preparing a surface by clearing or grading the underlying dirt, peat, or clay subsoil into a roadbed, and then applying a layer of gravel to the prepared surface to form the roadway surface.
This method of road construction does not work well in marshy or wet areas. Greater amounts of gravel must be applied to the surface to provide a roadway of desired firmness, and the road's use life is very short in such areas. As the roads are driven upon by motor vehicles, some of the gravel is displaced to the outside of the road. Other gravel is embedded by the weight of the vehicles into the subsoil. The embedding process occurs more quickly when the subsoil is wet. As time passes the gravel becomes so deeply embedded in spots that patches of the subsoil appear on the road surface. This process is commonly referred to as "mixing". These patches become very muddy during rainstorms and soon holes or ruts in the road appear where the gravel has been worn away and/or deeply embedded.
An asphalt layer is sometimes applied over the gravel surface of the road to prevent slippage of the gravel and to lengthen the life of the road. The gravel, however, is still able to embed into the subsoil, and this may lead to cracks in the asphalt and to the appearance of potholes which require prompt repair.